1. Field of Invention
The present invention relates to a differential reference voltage generator. More particularly, the present invention relates to a differential reference voltage generator applied to an analog to digital converter.
2. Description of Related Art
In general, a pipelined analog-to-digital converter (ADC) is a multi-step quantizer, in which a plurality of ADCs are cascade-coupled with one another, and in which each of the ADCs has the same or similar configurations with one another. A conventional pipelined ADC includes a plurality of stages, and each of the stages includes a sample-and-hold (S/H) circuit, a digital-to-analog converter (DAC), and a residue amplifier; furthermore, a reference voltage driver is employed in the conventional pipelined ADC for providing the differential reference voltages to those circuits.
The stability of the differential reference voltage directly affects the performance of the pipelined ADC, therefore, a precise differential reference voltage is required for driving capacitors in each of the pipelined ADC stages, so that the pipelined ADC can operate precisely. However, the differential reference voltages vary as the power supply voltage changes due to the progress of the manufacture process, which might cause the pipelined ADC operates abnormally.
Hence, there is a need for a new differential reference voltage generator which can produce stable differential reference voltage and can make the pipelined ADC operate normally.